As shown in FIG. 4, the conventional keyswitch 20 generally comprises a base plate 71, a printed circuit board 72, an insulating membrane 73, an elastic member 74, a key support mechanism 75 and key 76. The key support mechanism is formed by pivotally joining a first support lever 751 and a second support lever 752 in a scissors-form. However, as also shown in this figure, the shape and the structure of these two support levers are different, wherein the first support lever 751 is of .quadrature. shape and the second support lever 752 is of U shape, and the first support lever 751 is arranged between two arms of the second support lever 752. Therefore, two set of different molding dies are required to designed these two support levers. The cost is hard to reduce. Moreover, the orientation and order of the support levers 751 and 752 should be careful during assembling. For example, the support levers 751 and 752 may be assembled with the same or the opposite orientation. The assembling efficiency is therefore degraded.
Moreover, the conventional keyswitch generally has a stop pole formed by pressing at the pivoting groove 711 of the base plate 71 when the support levers 751 and 752 are pivotally connected to the base plate 71. The stop pole 712 is used to restrain the bump 753 of the support lever 751. However, the stop pole 712 is only provided at the center (as shown in FIG. 4) of the base plate 71, the support lever is wont to shake laterally and hard to be stably fixed on the base plate 71. Moreover, through hole must be formed between the stop pole 712 and the base plate 71, the openings 721 and 731 on the stop pole 712 and the base plate 71 is forced to be enlarged.
Moreover, as shown in FIG. 5, the key 76 is conventional keyswitch has pivoting recess 761 and sliding groove 762 for the pivotal engaging of the pivot shaft 754 and 755 of the support levers 751 and 752, respectively. The pivoting recess 761 is generally formed by two retaining arms 763 and 764, as shown in FIG. 4, which is separated by a predetermined distance to clamp the pivot shaft 754 of the support lever 752. However, the pivot shaft 754 is wont to release because the retaining arms 763 and 764 only clamp one forth length of the pivot shaft. The two retaining arms 763 and 764 are wont to break because they have the same thickness.
It is the object of the invention to provide an improved keyswitch to overcome above problems.
In one aspect of the invention, the inventive keyswitch comprises a base plate, a conductive membrane, an elastic member, a key support mechanism and a key wherein the first support lever and the second lever of the key support mechanism are of the same structure and pivotably joined in a scissors-form. The molding die can be simplified, the assembling efficiency can be enhanced and the cost is reduced.
In another aspect of the invention, the inventive keyswitch has pivoting recess formed by two retaining walls separated by such distance that the pivot shaft of the support lever is just fitted therebetween. A hook is formed on the free end of one of the retaining walls and has length exceeding the half length of the pivot shaft. The other one of the retaining walls has thinner thickness such that it has flexibility to shift outward to prevent the break thereof.
In still other aspect of the invention, two stop poles separated by a predetermined distance are formed on one side of the pivot recess on the base plate to prevent the release of the pivot shaft retained within the pivot recess. The stop poles has chamfered edge to facilitate the insertion of the pivot shaft and has augmented number to more firmly retain the pivot shaft of the support lever and prevent the lateral movement of the pivot shaft.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: